As a fixing device for thermally fixing a developer image onto a recording sheet such as a sheet of paper, there is conventionally known one that includes an endless fusing belt, a nip member disposed in an internal space of the fusing belt, and a backup member such as a pressure roller that nips the fusing belt in cooperation with the nip member. In the fixing device having such a configuration (hereinafter referred to as first conventional fixing device), lubricant is provided between the fusing belt and the nip member in order to enhance slidability between the nip member and the circularly moving fusing belt.
Further, typically, an electrophotographic-type image forming apparatus includes an image carrier, a transfer member, and a fixing device. The image carrier is capable of carrying thereon an image formed by a developer such as toner. The transfer member transfers the developer image carried on the image carrier onto a recording sheet. The fixing device thermally fixes the transferred developer image onto the recording sheet. As such a fixing device, there is known a fixing device of a type (hereinafter referred to as a second conventional fixing device) in which an endless belt (fusing film) is nipped between a nip member disposed at a side of an inner peripheral surface of the endless belt and a rotatable body (pressure roller) disposed at a side of an outer peripheral surface of the endless belt. In the second conventional fixing device, while a recording sheet carrying a developer image is nipped and conveyed between the belt and the rotatable body, the developer is heated and melted to be fixed on the recording sheet.
There is known a configuration adopted by the second conventional fixing device, in which a flow guide groove is formed on a contact surface of the nip member that is brought into sliding contact with the belt in order to uniformly disperse lubricant used for enhancing slidability between the nip member and the belt.